Such a method and an apparatus for carrying out the method are known, for example, from a system by the applicant for the precontrol and feedback control of a 12-cylinder spark-ignition engine which has two cylinder banks with each bank having six cylinders. The fuel-metering devices are designed as injection devices. The intake pipes are separated from each other, and there are two separate tank venting valves. The adapted precontrol and feedback control are carried out by two mutually separate individual apparatus, each apparatus being assigned to a respective cylinder bank.
A similar method as well as a corresponding arrangement is also disclosed in U.S. Pat. No. 4,383,515. However, here only one precontrol value dependent upon engine speed and load without adaptation is utilized and only the exhaust gases of the two cylinder banks having separate exhaust-gas probes are detected. Tank venting is not provided.
U.S. Pat. No. 4,683,861 discloses an arrangement for venting a fuel tank utilizing a lambda control as well as an adaptive precontrol. In this connection, the basic adaptation in the lambda control loop for the computation of the metered fuel is only then released when the quantities of fuel originating from tank venting are negligible.
Methods of the type mentioned at the beginning are referred to as stereo lambda control. The separate exhaust-gas channels with a lambda probe and a catalytic converter in each channel are characteristic of stereo lambda control. The exhaust pipes may be united downstream of the catalytic converter. The intake lines need not be completely separate from each other, as in the case of the exemplary application described, instead air may be taken in jointly for both banks through a main pipe.
Adapted precontrol and feedback control is understood as being the process by which precontrol values for setting the air/fuel mixture, as a rule preliminary injection times, are determined in dependence upon values of operating variables. The precontrol values are chosen such that a desired lambda value is to be specifically achieved in the particular operating state, especially the lambda value 1, in the case of lean concepts a lambda value greater than 1. If deviations from the desired lambda value occur, they are corrected. In order to allow for system-immanent disturbance quantities, an adaptation is also carried out, that is the precontrol values are corrected with integral results of the value of the feedback control manipulated variable. As a result, system deviations remain within narrow limits, which results in fast correction and a low tendency to oscillate of the arrangement for adapted precontrol and feedback control.
In the case of a stereo lambda control, individual disturbances, for example different air leakage rates and different through-flow rates of the fuel-metering devices, act on each of the two cylinder banks. According to the state of the art, allowance is made for this independence of the two cylinder banks from each other by the method for adapted precontrol and feedback control being carried out separately for each bank, in an apparatus provided separately for this in each case. This leads to a relatively high cost of the overall apparatus for stereo lambda control.